MOv18 – opening a new front for immunotherapy

By the time of this 2008 meeting, antibodies that bind specific antigens on cancer cells, causing recipients’ immune system to attack and destroy them, had become powerful treatment options for certain cancer types. And such antibodies have continued to emerge ever since. But all these therapies use immunoglobulin G antibodies.

IgG antibodies defend against infections. Whereas allergic reactions – from rashes to potentially fatal anaphylactic shock – are mediated by immunoglobulin E antibodies. And it was IgE that Karagiannis was proposing using.

She had shown in various mouse models that IgE is more potent than IgG at shrinking tumours. But those mice were immunocompromised. Surely giving a person with cancer an injection of IgE risked a huge, potentially fatal, allergic reaction?

But now, fifteen years on – and over quarter of century since this project began ­– the team has just published the results of the first ever clinical trial to administer an IgE to humans.

The CRUK-sponsored study – involving people with advanced gynecological cancers – showed that when combined with the right screening tests, this novel class of drug can safely be given to humans.

In one recipient, a markedly low dose of antibody showed clear signs of shrinking her tumour.

Spicer says the reason CRUK wanted to originally sponsor this work was that he and Karagiannis weren’t simply pitching a new cancer target, they were pitching a new type of drug.  Simply proposing a new target, he says, “was not going to open up a new hinterland of translational biology in the way that this trial has.”

Parasites, and the power of E

Karagiannis’s PhD supervisor was Hannah Gould, who cloned an IgE gene in 1982 then went on to become a world leader in allergy. As Gould’s lab deciphered IgE’s pivotal role in this maladaptive process, other groups showed this antibody type is also instrumental in defending against parasites, such as worms.

“This is something IgE does naturally,” says Karagiannis. “The immune system in the gut, in our muscles, in skin, can kill big parasites. It can really destroy them.”

But in the mid-1990s Gould’s interest in cancer was sparked by the emergence of monoclonal IgG antibodies as drugs, coupled with her keen appreciation of how IgE and IgG differ.

To trigger the destruction of an invading pathogen – or a cancer cell – antibodies must bind two things. Their antigen-binding domains must stick to proteins that distinguish the target. And their Fc domains must bind and activate receptors on the immune cells that will attack that target.

The existence of a high-affinity Fc receptor for IgE means these antibodies bind to immune cells much more avidly than IgG does. This causes sustained immune activation – plus maximal activation by only tiny amounts of IgE.

Additionally, allergy studies had shown that compared to IgG, IgE powerfully recruits a different set of effector cells – cells that Gould thought would be more effective at destroying cancer cells, especially in solid tumours.

In a departure from her established research interests, Gould asked her lab to run some pilot experiments to test these ideas.

Choosing to work on a model of ovarian cancer, the lab acquired an existing IgG, called MOv18. This antibody bound folate receptor alpha, an antigen that characterizes this tumour type, and it was known to have anti-cancer activity. Then, her lab made an IgE version of MOv18 and compared the two.

In the pivotal experiment, Gould’s team grew tumours in mice using an ovarian cancer cell line, then treated these animals with either MOv18-IgG or MOv18-IgE.

IgE shrank tumours more – and for longer.

While various lab members conducted these initial experiments, Karagiannis was completing her PhD on allergy. But then Gould asked her to take over the project. “I was the hired person to get that study over the line,” Karagiannis says. “Hannah considered me the person to move it forward.”

They published their first results in 1999, then Karagiannis developed the next model in which to test MOv18-IgE – from now on, simply MOv18. Using xenografts of patient-derived cancers implanted in mice, the results were the same: IgE was a much more potent anti-cancer agent than IgG.

But despite the lab’s excitement, funding was hard to come by. So much so, Karagiannis had to leave the lab in 2002 and take a job in industry. Her work there convinced her of the value of immunotherapies for cancer, but her heart remained with academia and IgE.

And when funding materialised in 2003, Gould invited Karagianis back. “Hannah said, ‘I’m giving you a postdoc but you’re not just coming for a postdoc. I’m going to look after you. You can take this on for your career’,” says Karagiannis. “Because Hannah’s lab was all about allergy and they didn’t want to diversify, she saw me as the person from the beginning. In many ways, Hannah believed in me more than I believed in me.”

Building the case

In late 2003, Karagiannis published the lab’s second paper on MOv18 describing the results in the xenograft model. Then, she worked on uncovering the mechanisms by which IgE induced the eradication of tumours. Papers in 2007  and 2008  confirmed that IgE recruits a unique set of immune cells and that activated monocytes are central.

This work helped Karagiannis secure a fellowship in 2007, which allowed her to begin transitioning to her own lab – and to focus on moving this work toward the clinic. Equally significantly, Spicer had joined King’s, and he and Karagiannis had instantly clicked.

“Industry,” he says, “was either afraid of this or didn’t understand.”

It is innovative projects exactly like this which CRUK, in general, and the Drug Development Unit, in particular, are set up to support. Even so, Sarah Mellor, who became the CDD’s project manager of MOv18 in 2010, says, “it was a big thing for us to decide to do it because nobody else would touch it with a bargepole.”

Mellor also says that by the CDD’s normal standards, “It came in at a very early stage.”

“But it was seen as a real potential game changer,” she says. “If we could do it, it would be a really significant step forward in cancer research. That was the real hook for doing the project.”

Getting to the clinic

Nigel Blackburn – who this autumn retired as director of the CDD – recently wrote that when he became leader of the unit in March 2009, he was immediately tasked with streamlining the department by drastically reducing the number of projects it supported – and that an air of scepticism still clung to IgE. On top of safety concerns, this being an entirely new class of therapeutic antibody meant that nobody had ever made clinical grade IgE before.

Blackburn credited a “small core of people in the department” with convincing him of the project’s merit and he pressed ahead with it. Looking back, Karagiannis says, “Clearly, Nigel fought our corner in a big way.”

Regarding manufacture, Mellor says, “It had to be done to a certain standard in order to satisfy the regulators,” so CDD took the lead on this, using CRUK’s in-house production facilities.

“My worst nightmare would have been that we would have had material produced that was perfectly good quality, but was inactive,” says Karagiannis.

Thankfully, the methods used for producing clinical-grade IgG largely applied to making high quality IgE, meaning CRUK could make IgE suitable for use in people – assuming that is, those antibodies could pass all the necessary safety and toxicology tests.

And this presented another potential banana skin.

As new drugs approach the clinic, it’s commonly demanded that they are tested in animals as closely related to humans as ethically possibly. But CRUK has a hard rule that it does not conduct research in non-human primates.

Once more, this set people on edge. But again, Karagiannis’s expertise in immunology was critical.

What’s fundamental for testing immunological drugs in animal models is not the evolutionary distance between the model species and humans, it is whether the antibody -reacts with its target antigen in both species. Therefore, Karagiannis wrote to a research facility that routinely worked with monkeys and requested some blood samples. The facility obliged – and when Karagiannis’s lab tested MOv18, they found inadequate cross-reactivity. Testing it in monkeys would be futile. If the antibody appeared to be safe in them, this could be an extremely dangerous false-negative.

Instead, experiments by Karagiannis – and by others in the field – showed that the IgE system of rats operates very similarly to that of humans. Therefore, she proposed creating a rat version of MOv18 and to do toxicology screening in these rodents.

Karagiannis says she made her case to the MHRA, in a four-and-a-half hour-long meeting, again basing her arguments on meticulous immunological reasoning. And once the MHRA consulted a specialist panel, they agreed to Karagiannis’s plan.

Deborah Josephs – then a clinical research fellow and now a Phase 1 investigator with Spicer –spearheaded the work that showed MOv18 was safe in rats, so likely safe in people and working closely with a contract research organization chosen by the CDD her data on safety were formally confirmed and therefore suitable for submission to the MHRA.

But Josephs didn’t only study toxicology. Using a cancer model in rats, she tested both safety and efficacy. And for good measure, further dissected the drug’s mode of action.

Gould and Karagiannis had always thought IgE could be safely used in cancer patients, because allergic reactions are triggered by IgE being activated by circulating, multivalent complexes of an allergen. And although tumours shedding large amounts of an antigen into the bloodstream could risk such a reaction, in the tumours being targeted, the antigen was mainly stuck to the cells’ surfaces – and if it was shed, it wasn’t in multivalent complexes.

Josephs research confirmed that MOv18’s tumour-destroying action does not mimic allergy.

“What we think we’re doing is waking up that part of the immune response that targets parasites,” says Karagiannis. In the case of an IgE antibody directed against tumours, this mechanism is critically dependent on activating macrophages within the cancer, and it involves the release of a distinctive profile of cytokines and other inflammatory messengers.

In fact, when the group looked at the survival rates of people with ovarian cancer, they saw that those individuals who had higher levels of these particular cytokines, lived longer. Thus, suggesting that intrinsic activation of an IgE immune response was naturally protective.

Of Josephs’ work, Spicer says, “To generate safety and efficacy data was a lot of experiments all rolled into one. There’s always a sort of killer experiment which gets you over the edge towards the clinic. And that was the data that really got us home and dry with the MHRA, the regulator.”

Finally, a trial

The CDD and King’s teams assembled a clinical trial application jointly and went together to defend it at the MHRA. The trial was approved in November 2015 – to run across multiple hospitals under the management of the CDD. And in February 2016, the first volunteer to ever receive an IgE drug was given MOv18.

This dose escalation study was designed primarily to test MOv18’s safety and tolerability. Across five, pandemic-disrupted years, twenty-six volunteers participated. Each had advanced or metastatic gynecological cancer: 21 were ovarian and all tumours expressed MOv18’s folate receptor alpha antigen. After treatment, participants were also screened for antitumor activity.